Cutting with VirtualDub: Key Frame

[cheerful]

For direct processing, the in point must be at a key frame. What about the out point? Thanks!

[guns1inger]

Both must be keyframes to avoid re-encoding. Check out the latest version of virtualdub, as I believe they were working on only re-encoding the last open GOP, although with Divx/Xvid this could still be up to 300 frames.

[cheerful]

By latest, do you mean experimental? I could not find release notes on their site.

Is there any explanation on why the re-encoding would happen? Are non-key-frames based on the previous key-frame? Is so, why removing all non-key-frames up till next key frame will affect frames prior to it?

Thanks!

[manono]

Beginning with the 1.7.0 version of Virtual Dub, from November 2006, VDub has had the "Smart Rendering" capability to which guns1inger referred:

Build 25854 (1.7.0, experimental): [November 5, 2006]
[features added]
* New "smart rendering" feature for selective processing of video around
edit areas while copying as many existing frames as possible.

I didn't quite understand the rest of what you wrote, but AVIs can only be cut on keyframes. If you don't have one where you want to cut, that small section between keyframes has to be reencoded to create one, so you can then cut where you want.

[jagabo]

Any segment you keep must start on a keyframe. The segment does not have to end on a keyframe. You probably can't end on a B frame.

[cheerful]

That is what I was asking. I am running 1.6.17. It seems (I am not 100% sure) that I have to keep all the frames b/w 2 key frames.

For example, let's say the frame sequence is I-P-P-P-P-P-P-P-P-P-P-I, I would think I could cut it to I-P-P-P-P-P w/o re-encoding.

Any segment you keep must start on a keyframe. The segment does not have to end on a keyframe. You probably can't end on a B frame.

[jagabo]

For example, let's say the frame sequence is I-P-P-P-P-P-P-P-P-P-P-I, I would think I could cut it to I-P-P-P-P-P w/o re-encoding.

Yes, I do it all the time.

[cheerful]

It seems that I can't cut

I-P-P-P-P-P-P-P-P-P-P-I-P-P-P-P-P-P-P-P-P-P

to (remove the last 5 P)

I-P-P-P-P-P-I-P-P-P-P-P

It always insert all 10P b/w the 2 I.

Which version are you using?

Thanks!

For example, let's say the frame sequence is I-P-P-P-P-P-P-P-P-P-P-I, I would think I could cut it to I-P-P-P-P-P w/o re-encoding.

Yes, I do it all the time.

[jagabo]

I usually use VirtualDubMod 1.5.10.1 these days. But I've been using various releases of VirtualDub, VirtualDubMPEG2, and VirtualDubMod for years. They all behaved the same way in this respect.

I just verified that mark-out can cut anywhere with VirtualDub 1.6.15, VirtualDubMPEG2 1.6.15, and VirtualDubMod 1.5.10.1 (the versions I have installed right now). I used both Xvid and Divx encoded AVI files in the tests.

I-P-P-P-P-P-P-P-P-P-P-I-P-P-P-P-P-P-P-P-P-P

to (remove the last 5 P)

I-P-P-P-P-P-I-P-P-P-P-P

It always insert all 10P b/w the 2 I.

Cutting off the last 5 P should leave

I-P-P-P-P-P-P-P-P-P-P-I-P-P-P-P-P

[DarrellS]

According to the Virtualdub help files, you have to start and end on a key frame but from my experience, as long as I start on a key frame then I can end it where I choose. All of my files have the key frames far apart though which may have something to do with my success.

Virtualdub is supposed to automatically adjust to the keyframes but if there isn't a keyframe to adjust to then it must accept your endpoint.

Since your file has alot of keyframes then it has to jump back to the last keyframe.

If your file had less keyframes it would probably chop exactly where you wanted.

Try choosing the AVI that you want to edit and put a check mark next to "Ask for extended options after this dialog" > click "Open" > put a check mark next to "Re-derive keyframe flags" and click "OK".

Virtualdub will recreate the keyframe flags and then you should be able to edit where you want.

Good Luck!

[cheerful]

Sorry. What I really meant to cut out the 5 P frames before the I frame. And do this many times in an editing session on 1 AVI file. The real editing is like

1. mark the starting point at a P frame.

2. mark the ending point at a I frame

3. Delete

4. Repeat 1-3

[jagabo]

Sorry. What I really meant to cut out the 5 P frames before the I frame. And do this many times in an editing session on 1 AVI file. The real editing is like

1. mark the starting point at a P frame.

2. mark the ending point at a I frame

3. Delete

4. Repeat 1-3

I'll have to check...

Works with VirtualDubMod 1.5.10.1.

[DarrellS]

I just figured out the best way to edit a file with very few keyframes in Virtualdub without having to recompress the video and making every frame a keyframe.

1. Open the file you want to edit.
2. Select File, File Information and check to see what codec is used.
3. Select Video, Compression and find the video codec that is used.
4. Edit the properties of that codec to make every frame (or every other frame) a keyframe.
5. Select Video, Fast Recompress and save new AVI. This should not affect the quality of the file.
6. Take new AVI and cut anywhere you want.